I. Technical Field
This disclosure generally relates to devices and methods for providing information to a user. More particularly, this disclosure relates to devices and methods for providing information to a user by processing images captured from the environment of the user.
II. Background Information
Visual acuity is an indication of the clarity or clearness of a person's vision that is commonly measured twenty feet from an object. When measuring visual acuity, the ability of a person to identify black symbols on a white background at twenty feet is compared to the ability of a person with normal eyesight. This comparison can be symbolized by a ratio. For example, a ratio of 20/70 vision means a person located at a distance of twenty feet can see what a person with normal vision can see at seventy feet. A person has low vision if he or she has a visual acuity between 20/70 and 20/200 in the better-seeing eye that cannot be corrected or improved with regular eyeglasses. The prevalence of low vision is about one in a hundred for people in their sixties and rapidly increases to one in five for people in their nineties. Low vision may also depend on the environment. For example, some individuals may be able to see only when there is ample light.
A person may have low vision (also known as visual impairment) for several reasons. Other than eye damage and failure of the brain to receive visual cues sent by the eyes, different medical conditions may cause visual impairment. Medical conditions that may cause visual impairment include Age-related Macular Degeneration (AMD), retinitis pigmentosa, cataract, and diabetic retinopathy.
AMD, which usually affects adults, is caused by damage to the retina that diminishes vision in the center of a person's visual field. The lifetime risk for developing AMD is strongly associated with certain genes. For example, the lifetime risk of developing AMD is 50% for people that have a relative with AMD, versus 12% for people that do not have relatives with AMD.
Retinitis pigmentosa is an inherited, degenerative eye disease that causes severe vision impairment and often blindness. The disease process begins with changes in pigment and damage to the small arteries and blood vessels that supply blood to the retina. There is no cure for retinitis pigmentosa and no known treatment can stop the progressive vision loss caused by the disease.
A cataract is a clouding of the lens inside the eye which leads to a decrease in vision. Over time, a yellow-brown pigment is deposited within the lens and obstructs light from passing and being focused onto the retina at the back of the eye. Biological aging is the most common cause of a cataract, but a wide variety of other risk factors (e.g., excessive tanning, diabetes, prolonged steroid use) can cause a cataract.
Diabetic retinopathy is a systemic disease that affects up to 80% of all patients who have had diabetes for ten years or more. Diabetic retinopathy causes microvascular damage to a blood-retinal barrier in the eye and makes the retinal blood vessels more permeable to fluids.
People with low vision experience difficulties due to lack of visual acuity, field-of-view, color perception, and other visual impairments. These difficulties affect many aspects of everyday life. Persons with low vision may use magnifying glasses to compensate for some aspects of low vision. For example, if the smallest letter a person with 20/100 vision can read is five times larger than the smallest letter that a person with 20120 vision can read, then 5× magnification should make everything that is resolvable to the person with 20/20 vision resolvable to the person with low vision. However, magnifying glasses are expensive and cannot remedy all aspects of low vision. For example, a person with low vision who wears magnifying glasses may still have a difficult time recognizing details from a distance (e.g., people, signboards, traffic lights, etc.). Accordingly, there is a need for other technologies that can assist people who have low vision accomplish everyday activities.